The present invention relates to means and procedures of energy storage in steam power plants for the purpose, on the one hand, of peak-load coverage by means of storage vessels with steam cushion and water content and, on the other hand, for stop-gap reserve. It makes possible continued operation of the steam turbine in case of failure of the steam generator.
There are already known in the art hot-water storage vessels which are connected parallel to the feed water preheater network and, in case of need during peak load or overload, supply the steam generator with preheated feed water. Their effect is based on the concept that the last or all stages of bleeding from the turbine are closed, so that there results in the low-pressure section of the turbine a higher mass flow than in the normal case and hence a higher than normal output.
This known layout has limited output, the maximum overload being achieved by completely closing the bleeds. Another disadvantage are losses resulting from the dependence of the bleeding pressures and hence of the feed water temperature on the load during charging and discharging. These losses result in a reduction of the storage efficiency. Furthermore, the layout pressure of the storage vessel is tied to the feed water temperature; this means, the layout pressure of the storage vessel cannot substantially exceed the saturation pressure corresponding to the feed water temperature. With previous steam power plants, feed water temperature and economically optimum storage pressure were adapted to each other. Recent developments resulted, on the one hand, in a reduction of the feed water temperature (as, e.g., with the light water reactors, the heavy water reactors or gas-cooled reactors); on the other hand, the development of prestressed storage vessels made it possible and economically meaningful to use high and highest storage pressure, so that the optimum storage pressure is much higher than the saturation pressure associated with the feed water temperature.
Another disadvantage of previous feed water storage is that in the absence of steam delivery, continued operation of the steam turbine is not possible. This disadvantage particularly affects nuclear power plants where, due to the generally high block power output, in view of the power grid, there must be an immediate stop-gap reserve (available within seconds or fractional seconds) for the reactor and steam generator; this also applied to solar-heat power plants where, in view of brief sudden interruptions of solar irradiation, e.g., by passing clouds, there must be a short-term stop-gap reserve and a longer-term stop-gap reserve to compensate for the solar radiation absent during the night.
The previously published constructions intended for stop-gap reserve have great disadvantages. Storage vessels designed as variable pressure storage vessels in case of steam withdrawal lose pressure quite rapidly and as a result the throughput capacity of the turbine and the capacity for doing work decrease rapidly; hence they cannot (or only at the price of a large power drop) be connected to the live steam line. Constant-pressure heat storage vessels (storage with water circulation) have the great disadvantage that steam delivery requires a certain time required for starting the circulating pump and for delivering the hot water to the flash tank or heat exchanger so that this type of storage also appears to meet the present-day high requirements for immediately available stop-gap reserve. With the so-called expansion storage vessel which, as the constant-pressure heat storage vessel, has a fairly constant pressure and where water is not circulated but is extracted from the storage vessel, flashed and then delivered to a low-temperature vessel, the time until steam delivery is too long for stop-gap reserve purposes.
Accordingly, it is an object of the present invention to provide an arrangement which avoids the disadvantages of storage vessels known in the art, while retaining their advantages.
Another object of the present invention is to provide an arrangement of the foregoing character which may be economically constructed and maintained in service.
A further object of the present invention is to provide an arrangement, as described, which has a substantially long operating life.